Role of interface configuration in diamond-related power devices

Durante los años transcurridos en el desarrollo de esta tesis, la generación de energía eléctrica mundial habrá crecido a un ritmo medio anual del 3.6%1, que refleja las crecientes necesidades de la sociedad en términos de suministro eléctrico (voltaje, densidad de potencia, frecuencia de uso, fiabilidad o temperatura de trabajo). Estas necesidades se están volviendo más exigentes, las pérdidas de energía deben ser reducidas y el rendimiento mejorado. El progreso de las recientes décadas en el campo de la electrónica de potencia no se debe sólo a la introducción de arquitecturas novedosas, sino también a la evolución de la composición de los dispositivos. El progreso actual está obstaculizado por las limitaciones inherentes al silicio, componente del que están fabricados la mayor parte de los dispositivos electrónicos de potencia actualmente disponibles comercialmente. Los semiconductores de ancha banda prohibida tienen propiedades particularmente atractivas para funcionar a altos voltajes y frecuencias en entornos de alta temperatura. Como semiconductores de ancha banda prohibida, los dispositivos basados en diamante semiconductor se han manifestado como un campo de investigación prometedor, no sólo por la amplia aplicabilidad en las ciencias biológicas, si no por sus extraordinarias propiedades eléctricas (elevada movilidad de portadores, alto valor de ruptura eléctrica y extraordinaria conductividad del calor). Tras casi quince años de investigación en diamante semiconductor se han resuelto gran cantidad de interrogantes, lo que ha permitido la aparición de los primeros prototipos. Es esta evolución en el conocimiento la que ha posibilitado la elección del diamante como candidato idóneo para la realización de componentes electrónicos de alta potencia, entendiendo estos dispositivos como aquellos que funcionan en condiciones de alta frecuencia de conmutación de señal. Paradójicamente, a pesar de sus numerosas ventajas y de los amplios estudios en esta materia, la explosión de las tecnologías basadas en diamante aún no ha llegado a su madurez. Esto es debido, fundamentalmente, a la mala calidad estructural en la implementación de los diseños ideados para los dispositivos electrónicos con canal activo de diamante. Adicionalmente, las limitaciones en las aplicaciones tecnológicas del diamante derivan de otras de sus propiedades extremas, como la dureza (que dificulta su clivaje) o la alta energía de activación de dopantes tipo n. Sin embargo, se han conseguido numerosos progresos en el crecimiento de estructuras de diamante para dispositivos eléctricos. En particular, estos esfuerzos han permitido minimizar la densidad de dislocaciones producidas durante el crecimiento de estructuras 1 OECD, library: http://www.oecd-ilibrary.org/economics/oecd-factbook-2013_factbook-2013-en 9 multicapa u optimizar la densidad de dopantes activos durante el crecimiento de capas dopadas (lo que ha requerido de amplios estudios sobre la incorporación del boro en la red cristalina del diamante). Paralelamente a los esfuerzos desarrollados en la comprensión y el estudio de la incorporación de dopantes en la red del diamante, se han desarrollado otros no menos loables avances en el diseño de estructuras óptimas para establecer contactos eléctricos en diamante. En la presente contribución, se evidencia el uso del diamante semiconductor como base para un dispositivo de alta potencia con canal activo de diamante, las diversas alternativas de diseño, sus técnicas de estudio y las características eléctricas de los primeros prototipos de los diferentes dispositivos.Ministerio de ciencia e innovación (becas FPI): BES-2010-039524 an

Diamond power devices: State of the art, modelling and figures of merit

With its remarkable electro-thermal properties such as the highest known thermal conductivity (~22W/cmbold dotK at room temperature) of any material, high hole mobility (> 2000cm2/Vbold dots), high critical electric field (>10MV/cm), and large bandgap (5.47eV), diamond has overwhelming advantages over silicon and other wide bandgap semiconductors (WBG) for ultra-high- voltage and high temperature applications (>3kV and >450 K, respectively). However, despite their tremendous potential, fabricated devices based on this material have not delivered yet the expected high-performance. The main reason behind this is the absence of shallow donor and acceptor species. The second reason is the lack of consistent physical models and design approaches specific to diamond-based devices that could significantly accelerate their development. The third reason is that the best performances of diamond devices are expected only when the highest electric field in reverse bias can be achieved, something that has not been widely obtained yet. In this context, high temperature operation and unique device structures based on the 2DHG formation represent two alternatives which could alleviate the issue of the incomplete ionization of dopant species. Nevertheless, ultra-high temperature operations and device parallelization could result in severe thermal management issues and affect the overall stability and long-term reliability. Additionally, problems connected to the reproducibility and the long-term stability of 2DHG based-devices still need to be resolved. This review paper aims at addressing these issues by providing the power device research community with a detailed set of physical models, device designs and challenges associated to all the aspects of the diamond power device value chain, from the definition of figures of merits, the material growth and processing conditions, to packaging solutions and targeted applications. Finally, the paper will conclude with suggestions on how to design power converters with diamond devices and will provide the roadmap of diamond devices development for power electronics.This work was supported by the U.K. Engineering and Physical Sciences Research Council for the University of Cambridge Centre for Doctoral Training under Grant EP/M506485/1 and by the French ANR Research Agency under grant ANR-16-CE05-0023 #Diamond-HVDC. The research leading to these results has been performed within the GREENDIAMOND project and received funding from the European Community's Horizon 2020 Programme (H2020/2014–2020) under grant agreement no. 640947

Diamond power devices: state of the art, modelling, figures of merit and future perspective

Abstract: With its remarkable electro-thermal properties such as the highest known thermal conductivity (~22 W cm−1∙K−1 at RT of any material, high hole mobility (>2000 cm2 V−1 s−1), high critical electric field (>10 MV cm−1), and large band gap (5.47 eV), diamond has overwhelming advantages over silicon and other wide bandgap semiconductors (WBGs) for ultra-high-voltage and high-temperature (HT) applications (>3 kV and >450 K, respectively). However, despite their tremendous potential, fabricated devices based on this material have not yet delivered the expected high performance. The main reason behind this is the absence of shallow donor and acceptor species. The second reason is the lack of consistent physical models and design approaches specific to diamond-based devices that could significantly accelerate their development. The third reason is that the best performances of diamond devices are expected only when the highest electric field in reverse bias can be achieved, something that has not been widely obtained yet. In this context, HT operation and unique device structures based on the two-dimensional hole gas (2DHG) formation represent two alternatives that could alleviate the issue of the incomplete ionization of dopant species. Nevertheless, ultra-HT operations and device parallelization could result in severe thermal management issues and affect the overall stability and long-term reliability. In addition, problems connected to the reproducibility and long-term stability of 2DHG-based devices still need to be resolved. This review paper aims at addressing these issues by providing the power device research community with a detailed set of physical models, device designs and challenges associated with all the aspects of the diamond power device value chain, from the definition of figures of merit, the material growth and processing conditions, to packaging solutions and targeted applications. Finally, the paper will conclude with suggestions on how to design power converters with diamond devices and will provide the roadmap of diamond device development for power electronics

Wide Bandgap Semiconductors Based Energy-Efficient Optoelectronics and Power Electronics

abstract: Wide bandgap (WBG) semiconductors GaN (3.4 eV), Ga2O3 (4.8 eV) and AlN (6.2 eV), have gained considerable interests for energy-efficient optoelectronic and electronic applications in solid-state lighting, photovoltaics, power conversion, and so on. They can offer unique device performance compared with traditional semiconductors such as Si. Efficient GaN based light-emitting diodes (LEDs) have increasingly displaced incandescent and fluorescent bulbs as the new major light sources for lighting and display. In addition, due to their large bandgap and high critical electrical field, WBG semiconductors are also ideal candidates for efficient power conversion. In this dissertation, two types of devices are demonstrated: optoelectronic and electronic devices. Commercial polar c-plane LEDs suffer from reduced efficiency with increasing current densities, knowns as “efficiency droop”, while nonpolar/semipolar LEDs exhibit a very low efficiency droop. A modified ABC model with weak phase space filling effects is proposed to explain the low droop performance, providing insights for designing droop-free LEDs. The other emerging optoelectronics is nonpolar/semipolar III-nitride intersubband transition (ISBT) based photodetectors in terahertz and far infrared regime due to the large optical phonon energy and band offset, and the potential of room-temperature operation. ISBT properties are systematically studied for devices with different structures parameters. In terms of electronic devices, vertical GaN p-n diodes and Schottky barrier diodes (SBDs) with high breakdown voltages are homoepitaxially grown on GaN bulk substrates with much reduced defect densities and improved device performance. The advantages of the vertical structure over the lateral structure are multifold: smaller chip area, larger current, less sensitivity to surface states, better scalability, and smaller current dispersion. Three methods are proposed to boost the device performances: thick buffer layer design, hydrogen-plasma based edge termination technique, and multiple drift layer design. In addition, newly emerged Ga2O3 and AlN power electronics may outperform GaN devices. Because of the highly anisotropic crystal structure of Ga2O3, anisotropic electrical properties have been observed in Ga2O3 electronics. The first 1-kV-class AlN SBDs are demonstrated on cost-effective sapphire substrates. Several future topics are also proposed including selective-area doping in GaN power devices, vertical AlN power devices, and (Al,Ga,In)2O3 materials and devices.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Diamond for Electronics: Materials, Processing and Devices

Progress in power electronic devices is currently accepted through the use of wide bandgap materials (WBG). Among them, diamond is the material with the most promising characteristics in terms of breakdown voltage, on-resistance, thermal conductance, or carrier mobility. However, it is also the one with the greatest difficulties in carrying out the device technology as a result of its very high mechanical hardness and smaller size of substrates. As a result, diamond is still not considered a reference material for power electronic devices despite its superior Baliga's figure of merit with respect to other WBG materials. This review paper will give a brief overview of some scientific and technological aspects related to the current state of the main diamond technology aspects. It will report the recent key issues related to crystal growth, characterization techniques, and, in particular, the importance of surface states aspects, fabrication processes, and device fabrication. Finally, the advantages and disadvantages of diamond devices with respect to other WBG materials are also discussed.The authors thank the Ministerio de Economia y Competitividad (MINECO) of the Spanish Government for funding under Grant Nos. TEC2017-86347-C2-1-R, ESP2017-91820, PID2020-117201RB-C21, and PID2019-110219RB-100 and the Junta de Andalucia (Andalusian Government, Spain) for funding through Nos. P20_00946, FEDER-UCA18- 106470 and FEDER-UCA18-107851 projects

GaN-based power devices: Physics, reliability, and perspectives

Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semicon- ductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spon- taneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high- voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench- structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main proper- ties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics

Wide Bandgap Based Devices

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

Development of Schottky and MOS interfaces for SiC power devices

The very nature of the wide bandgap semiconductor silicon carbide (SiC), namely its high critical electric field, thermal conductivity and stable native oxide, silicon dioxide (SiO2), has enabled the design, fabrication and market penetration of a new generation of power devices, Schottky barrier diodes (SBDs) and metal-oxide-semiconductor fieldeffect transistors (MOSFETs), with blocking voltages from 600-1700V. Despite the successful commercial realisation of these devices, the surface of SiC and the interfaces it forms with metals (Schottky interface) and insulators (MOS interface), are still the source of reliability problems such as premature breakdown and decreased lifetime of gate oxides on SiC. The focus of this thesis lies on the exploration of passivation approaches to the Schottky interface as well as the investigation of the quality of deposited gate oxides. Firstly, an electrical and physical analysis of the impact of a proposed phosphorous pentoxide (P2O5) treatment on planar and optimised 3.3 kV JBS diodes reveals a reduction of Schottky barrier height as well as leakage current, offering a possible path to overcome the basic trade-off between on-state and off-state performance of a diode. The second part of the thesis focuses on atomic layer deposition (ALD) – deposited SiO2 layers, where a post-deposition annealing (PDA) study reveals the performance improvement when a PDA in forming gas ambient at 1100°C is carried out. This process was then successfully transferred and validated on freestanding 3C-SiC material, which successfully demonstrated the general suitability of this material for power device applications

A walk on the frontier of energy electronics with power ultra-wide bandgap oxides and ultra-thin neuromorphic 2D materials

Altres ajuts: the ICN2 is funded also by the CERCA programme / Generalitat de CatalunyaUltra-wide bandgap (UWBG) semiconductors and ultra-thin two-dimensional materials (2D) are at the very frontier of the electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and deeper ultraviolet optoelectronics. Gallium oxide - GaO(4.5-4.9 eV), has recently emerged as a suitable platform for extending the limits which are set by conventional (-3 eV) WBG e.g. SiC and GaN and transparent conductive oxides (TCO) e.g. In2O3, ZnO, SnO2. Besides, GaO, the first efficient oxide semiconductor for energy electronics, is opening the door to many more semiconductor oxides (indeed, the largest family of UWBGs) to be investigated. Among these new power electronic materials, ZnGa2O4 (-5 eV) enables bipolar energy electronics, based on a spinel chemistry, for the first time. In the lower power rating end, power consumption also is also a main issue for modern computers and supercomputers. With the predicted end of the Moores law, the memory wall and the heat wall, new electronics materials and new computing paradigms are required to balance the big data (information) and energy requirements, just as the human brain does. Atomically thin 2D-materials, and the rich associated material systems (e.g. graphene (metal), MoS2 (semiconductor) and h-BN (insulator)), have also attracted a lot of attention recently for beyond-silicon neuromorphic computing with record ultra-low power consumption. Thus, energy nanoelectronics based on UWBG and 2D materials are simultaneously extending the current frontiers of electronics and addressing the issue of electricity consumption, a central theme in the actions against climate chang